1. Field
The present invention relates to radio receivers and more specifically to filtering received signals in radio receivers.
2. Description of the Related Art
The following description of background art may include insights, discoveries, understandings or disclosures, or associations together with disclosures not known to the relevant art prior to the present invention but provided by the invention. Some such contributions of the invention may be specifically pointed out below, whereas other such contributions of the invention will be apparent from their context.
Radio receivers may down convert a desired channel from an RF signal to a baseband frequency. The received RF signal may have unwanted frequencies, noise and interference, for example, that should be removed or attenuated to provide a signal with sufficient quality on the baseband frequency.
Also the radio receiver itself may cause noise to the received RF signal. This may be due to the type of integrated circuits used in the radio receiver or their quality. However, even with high quality integrated circuits noise may be introduced to the received RF signal if the operational voltage of the circuit is too low.
In radio devices that include many types of radios, for example a mobile phone with Bluetooth, WLAN (Wireless Local Area Network), GSM (Global System for Mobile Communications) and 3G (Third Generation Mobile Communications), the different radios may cause interference to each other.
Because many radio receivers are battery-powered, such as mobile phones, the power consumption of the radio receiver should be kept at an acceptable level. One factor affecting the power consumption of the radio receiver is the number of mixers that are used to mix the received RF signal. However, the power consumption may become high when a high number of mixers are provided a local oscillator signal. Furthermore, because of the several mixers that are interconnected, the pulse ratios of the local oscillator signals may need to be low so that the phases of the local oscillator signals to each mixer do not overlap.